The present invention relates to sequential lateral solidification (SLS).
One method of SLS, which may be referred to as the “2-shot process,” has been investigated for use in high-throughput processes. In this process, small beamlets, or a small beamlet, are projected onto regions of a silicon film overlying another substrate to induce melting and solidification (also referred to as “crystallization”) of large-grained polycrystalline silicon material. This may be referred to as a first shot. The small beamlets are then advanced and the process repeated such that the melted and solidified regions of this second shot overlap the regions of the first shot.
This process may be accomplished by using a single array of beamlets and making two or more passes over a given region of silicon film and microtranslating the array between passes. The process may also be accomplished by using multiple arrays of beamlets that are staggered with respect to each other and scanning the entire pattern in a across the silicon film. A single beamlet may also be used to iteratively stitch together crystallized regions, although this offers poor throughput.
The material produced using the above described process has severe directionality effects. The material has a plurality of narrow rectangular crystal grains oriented with the long axis perpendicular to the beamlet length.
As these directional effects are generally undesirable, a 2+2 process may be used to reduce, or eliminate, these directional effects. This may be accomplished by following up a first 2-shot process with a second 2-shot process carried out in a direction orthogonal to the first. This has been carried out by crystallizing silicon with an initial 2-shot process, rotating the sample being crystallized by 90 degrees, and then carrying out the second 2-shot process.
The need to rotate the sample by 90 degrees decreases throughput of the system, and adds complexity to the stage system for carrying out the SLS process.